As many as half of all individuals with psychiatric disorders also suffer from comorbid substance abuse. This is particularly true among individuals seeking treatment for combat-related posttraumatic stress disorder (PTSD), with the prevalence of comorbidity in this population estimated as high as 80%. These individuals suffer from an array of social, psychological, and medical problems, and are often refractory to treatment. Clinical observation suggests that a self-medication model of LSD and substance abuse may be heuristic. However, few data are available regarding the relationship between these disorders. The broad, long-term objectives of the proposed research are to understand the relationship between LSD and substance use disorders, and to contribute to the development of empirically-based interventions for individuals with both disorders. The specific aim of the proposed study is to test a central hypothesis of the self-medication model of comorbidity in PTSD: that intrusive recollections of the traumatic event trigger craving for alcohol among Vietnam veterans with comorbid LSD and alcohol dependence. The study will compare the effects of combat imagery, non-combat stress imagery, and neutral imagery on physiological and subjective measures of craving. Subjects will be 30 male Vietnam combat veterans. All subjects will meet criteria for LSD and alcohol dependence; patients with comorbid Axis I disorders or concurrent psychoactive substance dependence will be excluded. Subjects will be exposed to the imagery conditions in a repeated measures design. Each imagery trial will be followed by an alcohol cue exposure trial. Heart rate and self-reported distress will be used as manipulation checks to confirm the efficacy of the imagery manipulation. The study will be conducted in four individual sessions. In session one, subjects will complete structured interview and questionnaire measures, including information needed for the development of personalized imagery scripts and alcohol cue exposure trials. In sessions 2, 3, and 4, subjects will participate in the combat, noncombat stress, and neutral imagery conditions in counterbalanced order. Subjects will be seated in a private, sound-attenuated room. All instructions and auditory stimuli will be provided on a pre-recorded audiotape. After a 3-min baseline period, subjects will then insert dental rolls (for salivation assessment) and will be exposed to one of the three imagery conditions. Following imagery subjects will complete self-report measures of craving and distress. They then will the insert new rolls and undergo the alcohol cue exposure trial, followed by the self-report measures. Analyses of variance and covariance will be used for the primary data analyses examining the impact of imagery and alcohol cues on reactivity. Exploratory analyses will examine the role of cognitive and affective factors as potential mediators of the relationship between trauma imagery and alcohol craving. It is expected that the results will provide important information regarding the comorbidity of LSD and alcoholism, and will serve as a model for experimental research in dual diagnosis.